title: Genetic regulation: yeast mutants constitutive for beta-galactosidase activity have an increased level of beta-galactosidase messenger ribonucleic acid.
abstract: Mutants of Kluyveromyces lactis with elevated uninduced levels of beta-galactosidase (EC 32.1.2.3) activity, constitutive mutants (lac10c), were isolated and characterized to determine the basis for their constitutiveness. These lesions are not operator-type regulatory mutants because they are not closely linked to the beta-galactosidase structural gene. In a constitutive strain having a 7-fold increase in beta-galactosidase activity, the concentration of beta-galactosidase messenger ribonucleic acid (mRNA) was 8- to 10-fold higher than uninduced wild type. The half-life of beta-galactosidase mRNA was the same in the mutant strain (t1/2 = 4.5 +/- 0.2 min) as in uninduced wild-type cells (t1/2 = 4.8 +/- 0.1 min), indicating that the elevated mRNA level in the mutant was not due to a decreased rate of mRNA degradation. Consequently, we hypothesize that the LAC10 product regulates transcription of the beta-galactosidase gene; it probably affects the rate of transcription initiation. Parallel increases in enzyme protein, in constitutive levels of beta-galactosidase activity, and in mRNA further support this position, making translational or posttranslational control by LAC10 unlikely. Several types of data suggest that the LAC10 product functions as a negative regulatory element to prevent transcription. Other data demonstrate that lac10c mutations have pleiotrophic effects, there being constitutive levels not only of beta-galactosidase activity, but also the other lactose-inducible activities of galactokinase (EC 2.7.5.1), galactose-1-phosphate uridyl transferase (EC 2.7.7.10), and lactose transport. It would appear that LAC10 regulates lactose-inducible proteins.
mesh_terms: D002874:Chromosome Mapping; D005696:Galactosidases / Q000235:genetics*; D005786:Gene Expression Regulation; D005796:Genes; D005809:Genes, Regulator; D007785:Lactose / Q000378:metabolism; D009154:Mutation; D012333:RNA, Messenger / Q000378:metabolism*; D013696:Temperature; D014158:Transcription, Genetic; D015003:Yeasts / Q000235:genetics*; D001616:beta-Galactosidase / Q000235:genetics* / Q000378:metabolism
chemical_list: D012333:RNA, Messenger; D005696:Galactosidases; D001616:beta-Galactosidase; D007785:Lactose